docs: def _set_field_if_present(cls, block, name, value, attrs):
          """Sets the field block.name, if block have such a field."""
          if name in block.fields:
              value = (block.fields[name]).from_string(value)
              if "none" in attrs and attrs["none"] == "true":
                  setattr(block, name, None)
              else:
                  setattr(block, name, value)
          else:
              logging.warning("XBlock %s does not contain field %s", type(block), name)